Adaptation and self-fertilisation: from genes to genomes

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Why sex? Birds do it, bees do it, even educated fleas do it. Across the tree of life, sex is the predominant form of reproduction; explaining its prevalence has occupied some of the finest minds in evolutionary biology. Sexual reproduction can arise in various ways: in particular, many species are capable of self-fertilisation if they produce both male and female sex cells that can fertilise themselves to produce offspring. This form of reproduction is especially common in plants, but is also seen in many other organisms, including fungi, worms, pathogens, and some animals.This reproductive mode has a profound effect on how species can adapt to rapidly-changing environments, but we currently lack data regarding how genetic evolution is affected in species with this mode of reproduction. It was long thought that frequent self-fertilisation was an evolutionary 'dead-end', as it did not allow selection to efficiently remove unfit genes. However, mixed evidence exists for this theory, and it is also becoming apparent that high rates of self-fertilisation could also impede the fixation of adaptive genes. Understanding and quantifying how genetic evolution plays out in self-fertilising organisms will therefore shed new light on how organisms with different means of reproduction are able to adapt to rapidly-changing environments. This research topic also impacts on questions affecting society and agriculture. For example, many crops are highly self-fertilising, which enabled their rapid propagation after initial domestication. My goal is to unite state of the art mathematical analyses with genetic datasets, to create a complete picture of the process of adaptation in self-fertilising organisms. There will be two broad aims to my research. The first is to quantify what type of adaptation is prevalent in self-fertilising species. I will develop a suite of statistical methods to determine the prevalence, strength, and type of adaptation in selfing species. In particular, I will find out if adaptive genes arise from new mutations, or instead if they were created from either existing genetic variation that became adaptive following an environmental change, or recurrent mutation that reintroduces the new genetic variant. I will apply these models to data from a variety of organisms, including those that are important food sources for humans and animals.The second aim will be to carry out new theoretical studies to predict how self-fertilisation affects the evolution of multiple adaptive genes that are spread out throughout an individual's genome. I will first create mathematical models of how different degrees of self-fertilisation affect the spread of these genes if they act independently. I will next consider what happens if these adaptive genes then interact with each other, potentially favouring the appearance of fixed gene combinations and the spread of clones. I will finally determine how these phenomena feedback to affect the evolution of self-fertilisation itself.Overall, these techniques will help scientists understand what evolutionary forces underlie the appearance of self-fertilisation, and shed light on why reproductive modes are so diverse and flexible in nature.